Insulating or &#34;fish&#34; paper and method of making



y 6, 1935- J. L. M CLELLAN 2,008,141

INSULATING OR "FISH" PAPER AND METHOD OF MAKING V Filed'March 24, 1931 wy W Mv9/M4M Patented Jul 1c, 1935 2,008,141

UNITED STATES PATENT orrice INSULATING R FISH PAPER AND v METHOD 0]?MAKING James L. McClellan, Littleton, Mass, assignor to Hollingsworth &Vose Company, Boston, Mass, a corporation of Massachusetts ApplicationMarch 24, 1931, Serial N 0. 524,851 15 Claims. (Cl. 154-34) Thisinvention relates to papers which are escontrol of the paper-makingoperation, in ways pecially suitable for electrical insulating purposeswell known by those skilled in the art) that it preand the like and to amethod of'making the sents a relatively open, absorbent structure. same.Thus, for purposes of the present invention, the

5 Papers heretofore made for use in electrical open structure of thesheet is so controlled that 5 insulations have been prepared withrespect to subsequent impregnation, even by active reagents theimprovement of their electrical resistance or which tend to swell thecellulosic compounds of dielectric strength but such improvements havethe paper and thus close the interstices, may be usually been effectedat the expense of their effected to the desired degree throughout thephysical properties, such as mechanical strength, sheet. Other thingsbeing equal, it may be de- 10 toughness, flexibility, etc. Consequently,the insirable to employ a relatively more porous sheet sulating or fishpapers, so-called, which are when thick, and a less porous sheet whenthin. now available, are either of low dielectric strength In any event,the paper is especially charor of a weak, brittle, mechanical structure.acterized by a tough fibrous structure in which It is therefore anobject of the present inventhe original fibers have not been materially15 tion to provide an electrical insulating paper weakened and compose aconsiderable proporwhich shall have both a high dielectric or intion ofthe stock. In some instances, cellulosic sulating value and also a highdegree of mechanimaterials, which are subject to parchmentizing,

. cal strength or toughness, and which shall be may be added to providean additional matrix adapted to resist the strains of folding andshapbond g material for the tough fi s. but 20 ing as well as the wearincident to its subsequent the amounts of such materials should belimited use, without interruption of its structural conin order to avoidloss of strength in the finished tinuity. Other objects will appear fromthe folproduct. lowing disclosure. I It is further found that the papersheet thus It is found as a part ofthis invention that obtained may besubjected to a parchmentizing 25 fibers,-typicallythose derived fromlong fiber a n as y pass the S through a leaves namely the truehemps,.such as manila parchmentizing solution of sulfuric acid, zinc andsisal hemps, in contradistinction to jute'or chloride, or theIlka-preferably at such tembast fibers, and cotton, as well as straw andthe perature and for such time, in connection with like,--are not onlystrong and tough but may be the weight or thickness of the sheet, as toper- 30 formed into sheets of paper and so treated that mit thoroughpenetration of the sheet by the they shall preserve substantially theoriginal parchmentizing solutio'n,-the rate and degree strength of theindividual fibers and also acquire of the parchmentizing efiect beingcontrolled in a high dielectric strength or resistance to the part bythe concentration of the solution used.

passage of the electric current. 1 The treated sheet is then washed freefrom the 35 The fibers which are thus suitable belong geparchmentizingreagents, dried, and calendered nerically to the musaceee or bananafamily and to provide the desired thickness, density and fininclude morespecifically the fibers which are ish, according to known methods of the'paper known as manila and sisal hemps. These fibers making art. 40 areavailable in the form of the freshly pre- 'A typical instance ofcarrying out the inven- 40 pared material but are more commonly obtainedtion will be described with reference to the acas old rope which hasbeen made from these companying drawing, in which fibers. Common hempand jute, however, which Fig. 1 is a diagrammatic side elevation of vare bast fibers, are not suitable. suitable apparatus therefor; and 425The process of the present invention includes, Fig. 2 illustrates dryingand calendering equip generally, the reduction of the fiber or rope toment.

short lengths (e. g., two inches. more or less) For example, paper,which has been prepared which-are then beaten out to separate the fibersfrom sisal or manila hemp fibers, or both, as and may be subjected to analkaline cooking above described and which is ofarelatively opentreatment in a digester and underpressure for structure, is shown in theform of one or more a. sufiicient time to produce a pulp. This pulprolls,e. g., as indicated at l, 2, 3 and 4, respecmay then be formedinto an absorbent sheet of tively. These sheets may also containadditions paper in any of the customary ways for making of moreparchmentizable material, if desired, .manila fiber papers. Preferably,however, the such as cotton or other forms of cellulosic masheet is somade (by adjustments of the stock and terial, which has beenincorporated with the 5.

sisal or manila fiber in the beater. All four sheets may be composed ofsisal or manila fibers, for maximum strength in the finished sheet orone or more sheets may be composed of alpha cellulose or cotton fiber,if desired, for special purposes, such as to provide anjntervening layeror matrix of readily parchmentized cellulose. other numbers andarrangements of such sheets may also be provided for and integratedtogether, in like manner. r

The sheets are drawn, in parallel, into and through a tank 5 containinga parchmentizing solution,--e. g., a Baum solution ZIiClz in water,which is maintained at about F. The degree of penetration andparchmentizing effect of the solution upon the sheet may also becontrolled by the rate at which the sheets travel and the length of thetank. It may be still further regulated by passing each sheet through aseparate tank (not shown) having correspondingly prepared and regulatedparchmentizing solutions therein to effect the desired parchmentizingaction upon each sheet severally.

In passing through the tank (or tanks) 5% the sheets I, 2, 3 and 4, areguided by rolls 6, I, 8, 9 and H, l2, l3, l4,-and upon leaving theparchmentizing solution they are associated in intimate face contact.The composite sheet is then passed over a heated calender roll l5(preferably heatede. g., to 100 F.) and then between the upper roll l5and. the lower calender roll I6, which may also be heated, (e. g., toF.) In thus passing between the calender rolls, the

' sheets are integrated into a single sheet of substant-ially uniform,continuous structure. The

thus integrated sheet I! may be passed over spaced guide rolls [8,

19, 2|, while they are freely exposed to the air, thus permitting theparchmentizing action to become more completely effective throughout thesheet. By suitably spacing the rolls I8, l9 and 2|, the length of time,etc., of such aerating treatment" may be adjusted to the desired degree.

The sheet is then. subjected to a thorough washing treatment, which isefiected by passin through a long series of washing tanks 22,- 22, or

other appropriate apparatus. As shown, the sheet is conveyed,alternately over upper rollers 23, which may be connected to a suitablesource of power (not shown) to drive the same, and

under lower rollers 24, which are mounted near the bottom of thesuccessive tanks 22 of the series. These rollers are customarily mountedin frames (not shown) which may be raised from and lowered into thetanks, as desired, in order to thread and rethread the paper sheettherethrough. In operation, the tanks are periodically emptied-thecontents of the'first tank being withdrawn and the waste water from eachsucceeding tank being advanced. the last tank of the series being filledwith fresh water.

At the end of the series of washing tanks, the washed sheet may bepassed over a series of drying drums 26, 21, and thence through calendarrolls 28, if desired, and finally wound up in a roll, 29. whichconstitutes the finished product.

It is found that the parchmentizing treatment.

while substantially ineffective to soften or weaken the hard fibers ofthe type indicated, is never- 'lil theless sufficiently reactive upon aportion of the paper stock to provide a. bond between the tough fibersand also to fill the interstices, thus forming a 'relatively dense,impervious sheet. Moreover, this interfibrile parchmentized material ormatrix is characterized by high dielectric strength. At the same time,it is relatively soft and flexible, so that it preserves its continuityand bonding adhesion to the fibers in spite of repeated and drasticfolding.

If for any reason, the particular fiber emp yed does not contain asufficient amount of such bonding material or if it is not renderedavailable by the desired parchmentizing treatment, additions ofcellulosic materials which are especially susceptible to theparchmentizing treatment (preferably cotton pulp) may be madeadvantageously as pointed out above.

In either case, the strong and tough, undegenerated fibers form aninterlacing network throughout the paper sheet, imparting both strengthand toughness thereto which permit the finished sheet to be sharply bentor folded, without rupture on the stretched side of thefold nor bucklingor delamination in the compressed side of the fold. Consequently thecontinuity and structure of the sheet is preserved and its dielectricstrength as well as its mechanical strength remains unimpaired. That thepaper has an intrinsically high value in respect of these properties, ascompared with "fish paper heretofore produced is indicated by the dataobtained in tests upon paper made as above described in which it wasfound that:

(1) The dielectric strength (volts per mm. of thickness) is more thandoubled.

(2) The tearing strength (grams per millimeter of thickness) isapproximately doubled; and

(3) The folding strength (number of folds before rupture) is greatlyimproved.

Not onlyis the paper thusprepared stronger than the unparchmentizedsheet, but it is more resistant to abrasion and will not delaminate orseparate into the layers of which itis initially composed. If split, bycutting at the edge for example, and torn apart, it not only presentshigh resistance to such separation but does not tear continuously inthis plane. On the contrary the torn section tapers oil to the outersurface'of the sheet, and no evidence of an irregular or delaminatedstructure is observable.

Another feature of the product is a characteristic increase of tensilestrength upon wetting of the sheet with water, which continues withincreasing amounts of water up to such degree of saturation as it iscapable of.

While the resulting product is thus particularly advantageous for use asan insulating paper, it is clear. that its properties of strength,toughness, etc., and the preservation of these properties in spite ofrepeated folding or wear, make it especially applicable for many otherapplications and uses in which its dielectric properties may not be ofimportance.

Other modifications and adaptations of the method and applications ofthe product are therefore contemplated and are to-be considered asincluded by the following claims.

' I claim:

1. Method of treating paper, comprising as a step subjecting papercontaining true hemp fibers to a parchmentlzing treatment.

2. Method of making paper, comprising as steps preparing an absorbentsheet of paper from sisal and/or manila hemp fiber and subjecting thesame to a parchmentizing treatment.

3. Method of treating paper, comprising as a step subjecting papercontaining sisal and/or manila hemp fibers and additional cellulosicmaterial, to a parchmentizing treatment.

' 4. Method of making paper, comprising as steps fibers andcharacterized-by being parchmentized.

6. Paper, consisting substantially of sisal fibers and characterized bybeing parchmentized.

7. Paper, consisting substantially of manila fibers and characterized bybeing parchmentized,

8. Paper, containing true hemp fibers and other cellulosic material, andcharacterized by being parchmentized.

9. Paper, containing sisal fibers and other cel lulosic material, andcharacterized by being parchmentized.

10. Paper, containing manila fibers and other cellulosic, material,andcharacterized by being parchmentized.

11. Paper, characterized by containing true hemp fibers and a bondingmatrix of parchmentized cellulosic material.

12. Paper, containing true hemp fibers and a layer of cellulosicmaterial, the whole characterized by being parchmentized.

13. Paper, characterized by containing true hemp fibers and a layer ofother celluloslc material, said cellulosic layer being parchmentizecl.

14. Paper characterized by high dielectric capacity and flexibility, andcontaining sisal or manila hemp fibers and a bonding matrix ofparchmentized cellulosic material.

15. Paper characterized by high dielectric capacity and flexibility, andcontaining sisal or' manila hemp fibers and a layer of parchmentizedcellulosic material integrated therewith.

JAMES L. Mccnmmn.

